Efforts in the laboratory continue to study intrarenal cortical blood flow distribution and the effect such changes have upon renal sodium absorption. The role of prostaglandin E in maintenance of arterial blood pressure is being studied, particularly in the pregnant animal. Our hypothesis is that the elevated renin and angiotensin in both human and animal is necessary to maintain arterial blood pressure and results in a secondary rise in aldosterone secretion. Prostaglandin E in both pregnant animals and humans has been found elevated and the use of prostaglandin inhibitors causes hypertension in pregnant animals. Similarly, the use of an angiotensin antigonist, Saralasin, causes a significant fall in blood pressure in pregnant animals. Thus, the generalized smooth muscle relaxation which occurs during pregnancy may also involve arterioles causing a decrease in effective blood volume. In addition, recent studies have indicated that contralateral polyuria occurs following the increase in renin secretion accompanying either ureteral obstruction or renal artery stenosis. Although hypertension can cause reduced ADH secretion by activation of baroreceptors we have divorced this effect by preventing hypertension with the use of intravenous Arfonad after ureteral obstruction or renal artery stenosis. With no rise in blood pressure a rise in renin secretion causes contralateral polyuria with increase in CH2O. The same phenomenon occurs also in the hypothesectomized dog. Thus, we postulate that angiotensin is activating prostaglandin E synthesis in the contralateral kidney with antagonism of collecting tubular action of ADH. Further studies are now underway in which medullary prostaglandin synthesis is being studied in vitro and attempts will be made to correlate medullary synthesis rates with physiological changes in free water clearance. BIBLIOGRAPHIC REFERENCES: Chonko, A.M., Osgood, R.W. Nickel, A.E., Ferris, T.F., and J.H. Stein. Measurement of nephron filtration rate and absolute reabsorption in the proximal tubule of the rabbit kidney, J. Clin. Invest. 56:232, 1975. Venuto, R.C., O'Dorisio, T., Stein, J.H. and T.F. Ferris, Uterine prostaglandin E (PGE) secretion and uterine blood flow in the pregnant rabbit. J. Clin. Invest. 55:193, 1975.